It is thus the object of the present invention to create a method and a device for quality-testing fiber-reinforced plastic components with a thermoplastic matrix, which method and device with the use of simple technical means make it possible to examine the internal quality of the plastic components precisely and in a time-efficient manner.
The object is met on the basis of a method according to the precharacterising part of claim 1 in conjunction with its characteristic features. From the point of view of device technology, the object is met by claim 6. The respective related dependent claims state advantageous improvements of the invention.
The invention includes the process-related teaching according to which by means of an optical sensor unit the surface roughness of the plastic component is measured after forming, which surface roughness is analyzed by means of a downstream evaluation unit by a comparison with a stored reference pattern in such a manner that increased surface roughness is interpreted as increased internal materials porosity.
In other words the invention is based on analyzing a formed thermoplastic fiber-reinforced plastic component with reference to the surface roughness as to whether the interior quality of the plastic component has been diminished by the forming process. This represents a departure from directly examining the internal quality when assessing the internal quality. According to the invention, assessing the internal quality instead takes place on the basis of the external appearance of the plastic component. Since, with the use of data processing, optical acquisition and evaluation of the surface of a component by means of sample comparison can be effected very quickly in relation to the entire surface, very considerable time savings in the quality control can be achieved. Furthermore, no particular coupling between the sensor unit and the plastic component to be examined is required; in particular in contrast to ultrasound examination no liquid couplant needs to be used, and consequently the solution according to the invention is easier to implement from the point of view of equipment used. Standard components can be used for optical analysis. With the use of optical analysis, inferior internal quality can be deduced from a visibly rougher external surface than is the case in a fault-free plastic component. It has been observed that internal material separation and porosity manifest themselves as increased surface roughness on the plastic component. The invention thus uses this correlation between the surface and the internal quality.
As a particularly preferred measuring principle for implementing the method described above, optical strip reflection (reflectometry) is proposed. In this optical measuring method a strip pattern with luminous strips that are arranged straight and parallel and spaced apart from each other is generated by a radiation source, which strip pattern is projected onto the surface of the plastic component as the measurement object and is reflected from this surface. Due to the surface roughness the reflected strips are deformed. The deformed strips are acquired by a camera and are evaluated, by way of image analysis, in terms of surface angle, curvature and the like, in order to in this manner obtain conclusions relating to the distribution and the degree of surface roughness.
In the application of this measuring principle, which application forms the subject of the invention, it is proposed that the sensor unit comprises an LCD monitor for generating said strip pattern Immediately beside the aforesaid, and aligned in accordance with the optical axes, a CCD camera should be arranged for imaging the strip pattern reflected from the component surface. It is also possible to provide several sensor units in order to examine the plastic component simultaneously from several sides.
According to a preferred embodiment of the device according to the invention, a single sensor unit is, however, sufficient, which sensor unit is installed so as to be stationary, whereas by means of handling equipment the plastic component to be examined can be positioned so as to be flexible relative to the sensor unit. In this arrangement the handling equipment can be an industrial robot that can be moved along several spatial axes, which robot is present anyway, during the manufacturing process of the plastic component, for placing and removing the plastic component in or from the forming tool of the press.
By means of such a device the plastic component can be positioned in such a manner relative to the optical sensor unit that optical measuring can take place from several sides. Preferably, all the sides and thus the entire surface of the plastic component are optically measured in order to carry out a complete quality check. However, it is adequate if only those faces of the plastic component are optically measured, on which faces, based on experienced, reduced internal quality of the plastic component manifests itself by increased surface roughness. By means of this measure the time required for inspection can be further reduced.
According to another measure improving the invention, it is proposed that the stored reference pattern is generated in such a manner by way of the optical sensor unit that a sample component with normal surface roughness is optically measured by said optical sensor unit. The data measured in this manner is stored as a type of image file in a storage unit of the evaluation unit, which is preferably designed as a computer (PC).
In order to carry out an unequivocal inspection, according to another measure improving the invention it is proposed to determine a threshold value relating to the surface roughness of the plastic component. If, after implementation of the comparison of the measured surface roughness with the stored reference pattern, this threshold value is exceeded, as part of an automated quality inspection a good/bad selection of the plastic components to be checked can be made. In this manner an unequivocal and uniform inspection result can be achieved.
The solution according to the invention provides the conditions for the optical sensor unit to be able to detect local changes in the surface roughness relating to the overall surface of a measured face of the plastic component. If locally there is increased surface roughness, from this, locally inferior internal quality of the plastic component can be deduced.